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Martec is recomending a 12x6x7/8 MKIII folding prop for an Atomic four on a C&C M3.
Any suggestions? It is the only folding prop I could possibly afford. I have hard good things about them, but size and pitch ratios are critical to engine performance.
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Tell Martec that you want an 11 x 5 x 7/8 folding prop..that is what I have on my MKlll. It allows the Atomic four to run a little faster , thus less loading. It will push the boat along at 5.5 knots on an easy throttle without using a lot of fuel. The other benfit is that you have just a little more power during rough conditions.
Everyone I know has changed from a 6 or 7 pitch to a 5 and likes it.
'IRIS'
1975 C&C 27 Mk lll
Hull # 453
Kittery Point, Maine
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Last edited by (2009-03-04 03:40:46)
'IRIS'
1975 C&C 27 Mk lll
Hull # 453
Kittery Point, Maine
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Thanks for the feedback! I was thinking that an 11" diameter would be better and seem to have heard that 5" pitch might be more than enough. It helps when I know that is the exact configuration you are running. How is it in reverse?
Bjarki
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Reverse with a folding prop..never thought of it. Actually, it does work, but takes while to really engage as you are working in the direction of the folding blades. I find it best to preplan a bit and come to a full stop before backing, if nothing else start the reverse really early.
'IRIS'
1975 C&C 27 Mk lll
Hull # 453
Kittery Point, Maine
'IRIS'
1975 C&C 27 Mk lll
Hull # 453
Kittery Point, Maine
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I am running a Martec Folding that is 13 x 8, which is the size and pitch recommended by C&C in the owners' manual. This has led to some interesting performance issues: in relatively flat water, Carriden cruises at 5.5 to 6 knots while only turning 1440 RPM. Great power and excellent range from only sipping gas. Also, I have never felt that I needed to worry about my power in reverse. There is no lugging or other problems from the engine, but the oil pressure never gets very high (usually about 20 to 25 PSI). The down side to all that thrust is that when coming into harbour, I throttle down to 800 RPM and the boat is still doing 3-1/2 to 4 knots. Parading into harbour after a race involves a lot of slipping into and out of gear.
Still, the setup has worked well for years and I am fairly happy with it. If I were replacing the prop today, I might consider a lesser pitch, if only to allow for higher RPMs and finer control on the speed.
Marcus from Carriden
Mk III, Hull #847
Oakville, Ontario
Marcus Opitz,
Formerly from Carriden, Mk III, Hull #847,
now skippering "Everdina," a 1975 Ontario 32
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I had a privilege to helm Carriden on several occasions and was stunned with thrust and crusing speed Marcus folding propeller provides. I opted ($200 on eBay...I could not resist not to purchase one) to go with 12Dx7P Martec Eliptec folding propeller. This propeller is an inch bigger in its diameter than fixed one that was previously on the boat. Folding propeller hub is bigger than fixed and in my assessment I have actually replace size to size. I will report back its performance as soon as boats get into the water. By the way 11Dx7P fixed worked like a charm and at 800-900 rpm’s cruise at 0.5 knots in calm water.
Ivan
MKIII, Hull # 718
Oakville, Ontario
C-Wolf
Last edited by (2009-03-06 12:48:08)
C-Wolf
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>This propeller is an inch bigger in its diameter than fixed one that was previously on the boat. Folding propeller hub is bigger than fixed and in my assessment I have actually replace size to size.
I'm with you on the importance of acknowledging the hub size; blade length and pitch are the important variables (the additional leverage of having a larger hub and thus having any given blade 1/2" farther from the shaft is too hard to visualize). Plus, given the way blades are shaped, only the outer half has any significance, so in my mind, Towser's new 14" dia prop is only 1" dia larger than our original 12" dia prop (pitch is very different, and that to my thinking is where the real difference lies).
Look forward to hearing about you and Marcus drag-racing on flat and rough water at a range of revs for the props page in Black Arts.
David Weatherston
Towser, Toronto
C&C 27 Mk IV
David Weatherston
Towser, Toronto
C&C 27 Mk IV
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I had a Michigan "Blue Dot" 12X5 folder that I think was original to the boat (based on the builders file). I had a failed strut and some other issues, so I wanted a properly balanced prop to go with the new shaft, coupling, strut... I was not unhappy with this prop as far as performance, only vibration. I tried to find someone to balance the old folding prop without success. I finally bought a used (and not very pretty) Martec 11X5 folder and then had Martec rebuild it. They will rebuild a prop to “like new” for a reasonable price, I think it was $175 all told to have them rebuild it.
I really like the 11X5 and get about 1800 RPM from the direct drive atomic 4. I can run at 7+ knots flat out and throttle back a bit for gas savings and run 6 knots all day. I should maybe note that this is the older style Martec with the more flat ends on the blades, the out end of the blade is the part of that matters, so a new “elliptical” blade at 11X6 may not be that different as there is less blade out at the end with the tapered end elliptical. Reverse is less than great, but acceptable...
Bob Wooden - Rhapsody C&C 27 Mk 3
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